Is there a substitute for the cane sugar? Why use unsalted butter in a recipe?

You could put 1/2 to 1 tablespoon of brown sugar in the bottom of the 1/4th cup before adding granulated sugar to better mimic the flavor of the unwashed cane sugar.

Unsalted butter lets the cook control the saltiness of the food, since there is no industry standard for the amount of salt in butter -- it varies from brand to brand. As for the sugar, the unbleached cane sugar is closer to a natural state. Regular sugar won't replicate the exact flavor, but will be fine in the recipe.